Tropical Update: September 6th; 5:20p.m EDT

By: MiamiHurricanes09 , 9:15 PM GMT on September 06, 2011

Tropical Depression 14
As of 5p.m EDT the NHC has begun issuing advisories on the tropical wave associated with a well-defined low pressure system in the far eastern Atlantic. Latest satellite images reveal an organizing cyclone with convective banding starting to wrap around the well-defined low pressure system. The cyclone is an environment of favorable upper-level wind shear and surrounded by a moist mid-level atmosphere, and due to this I anticipate gradual intensification over the next few days.

The cyclone is currently cruising towards the west/west-northwest under the zonal flow courtesy of the subtropical ridge. This direction in heading is forecast to persist throughout the next 5 days placing the cyclone near the northern Leeward islands in the aforementioned time frame.

Upper-level winds are not forecast to increase more than 15 knots over the next 5 days and mid-level dry air is also forecast to remain low. Due to this I believe that the NHC forecast intensity is a little too low, and that 14L will reach hurricane status in 72-96 hours rather than 120 hours.

Plus, she's the most beautiful tropical depression I've seen in a long time (lol)...so I'd definitely be keeping a close eye on her if I lived in the northern Leeward Islands, the U.S VI, and the eastern Greater Antilles.


Figure 1. Infrared satellite image of 14L valid 20:49UTC, or 4:49p.m EDT.

Hurricane Katia
Hurricane Katia is starting to meet her demise. The eyewall replacement cycle that has been taking place throughout most of the day appears to be nearing completion, however atmospheric conditions no longer seem to be conducive enough for re-intensification.

The cyclone is moving towards the northwest under the influence of the southwestern periphery of the subtropical ridge. This direction in motion should persist throughout the next 36 hours or so, with a meridional turn thereafter. Beyond 72 hours the cyclone should begin to encounter the mid-latitudinal westerlies, which will induce a northeastward to east-northeastward turn along with a rapid increase in forward speed. I believe that Katia has reached her maximum intensity, however, she will probably maintain her current maximum wind speed value throughout the next 12-24 hours. Beyond 24 hours gradual weakening is anticipated.

The main threat from Katia continues to be dangerous rip currents along Bermuda and the eastern seaboard.


Figure 2. Visible satellite image of Hurricane Katia valid 20:49UTC, or 4:49p.m EDT.

Invest 96L
Convective activity over the past few hours in association with 96L has weakened considerably. This really doesn't come as a surprise with the behemoth amount of extremely stable dry air that lies to the northwest of the system. In the 96L's defense, however, an upper-level anticyclone has developed directly atop its vorticity maximum, which is only allowing for 5-10 knots of upper-level winds to impede upon the system.

I still strongly believe that the chances for development over the next 48 hours are low...about 10%. I'll have a more in-depth analysis on 96L tomorrow afternoon so be on the look-out for that.


Figure 3. Visible satellite image of Invest 96L valid 20:58UTC, or 4:58p.m EDT.

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23. aquak9
11:13 PM GMT on September 06, 2011
well, I thought it was 55W, but seems like folks were arguin' the point earlier this summer. Thanks for clearing that up.
Member Since: August 13, 2005 Posts: 199 Comments: 29600
22. MiamiHurricanes09
10:19 PM GMT on September 06, 2011
Quoting TropicalAnalystwx13:


You are mistaken, it is 55W. :P
Yeah yeah...whatever. :P

Quoting SouthDadeFish:
The GFS vortex of the system is only a small part of the overall SHIPS algorithm. It is at least a contributing factor.
The 00z runs tonight will help us determine if it's the initialization that has been off, since we now have a developed tropical cyclone.

Quoting TropicalAnalystwx13:
Oops, almost forgot, lol.

Thanks for the blog Miami!
No problem man LOL.
Member Since: September 2, 2009 Posts: 131 Comments: 21689
21. TropicalAnalystwx13
10:16 PM GMT on September 06, 2011
Oops, almost forgot, lol.

Thanks for the blog Miami!
Member Since: July 6, 2010 Posts: 128 Comments: 35751
20. TropicalAnalystwx13
10:12 PM GMT on September 06, 2011
Quoting MiamiHurricanes09:
I believe it's 50%u02DAW, but I might be mistaken.


You are mistaken, it is 55W. :P
Member Since: July 6, 2010 Posts: 128 Comments: 35751
19. SouthDadeFish
10:09 PM GMT on September 06, 2011
The GFS vortex of the system is only a small part of the overall SHIPS algorithm. It is at least a contributing factor.
Member Since: August 12, 2007 Posts: 11 Comments: 2449
18. MiamiHurricanes09
10:09 PM GMT on September 06, 2011
Quoting aquak9:
and we gotta wait till what, 55 or 50? before the HH can get to TD14?
55W it is...LOL.
Member Since: September 2, 2009 Posts: 131 Comments: 21689
17. MiamiHurricanes09
10:07 PM GMT on September 06, 2011
Quoting SouthDadeFish:
Thanks for the update. I want to agree with you about TD 14 strengthening more than the models are indicating because that is what intuition tells me, but from my experiences when the models aren't very ho-hum about a disturbance there is a good reason. I'm still trying to figure out the reason. I doubt it is dry air, but perhaps some sort of shearing. I know the SHIPS isn't really showing that much shear so I question this reason as well. I do think to some extent the models aren't initializing TD 14 that well either, which may explain why they aren't that aggressive. I found it interesting that SHIPS is giving a pretty high chance of rapid intensification, although it strengthens TD 14 pretty slowly. Here is the 18Z chances:

Prob of RI for 25 kt RI threshold= 41% is 3.2 times the sample mean(12.8%)
Prob of RI for 30 kt RI threshold= 19% is 2.2 times the sample mean( 8.4%)
Prob of RI for 35 kt RI threshold= 11% is 2.2 times the sample mean( 5.0%)
Prob of RI for 40 kt RI threshold= 7% is 1.9 times the sample mean( 3.4%)
You definitely have a point. When our best global models don't develop something, there's definitely something up.

The SHIPS has been losing 14L's vortex, hence the slow intensification rate. What's interesting however is that the LGEM doesn't intensify it that quickly either, so there definitely has to be something that they're seeing that we aren't.

I guess time will tell, but it is important that the northern Leeward Islands, the U.S VI, and the eastern Greater Antilles pay close attention and prepare for some (possibly intense) tropical weather come the weekend.
Member Since: September 2, 2009 Posts: 131 Comments: 21689
16. SouthDadeFish
10:00 PM GMT on September 06, 2011
Thanks for the update. I want to agree with you about TD 14 strengthening more than the models are indicating because that is what intuition tells me, but from my experiences when the models aren't very ho-hum about a disturbance there is a good reason. I'm still trying to figure out the reason. I doubt it is dry air, but perhaps some sort of shearing. I know the SHIPS isn't really showing that much shear so I question this reason as well. I do think to some extent the models aren't initializing TD 14 that well either, which may explain why they aren't that aggressive. I found it interesting that SHIPS is giving a pretty high chance of rapid intensification, although it strengthens TD 14 pretty slowly. Here is the 18Z chances:

Prob of RI for 25 kt RI threshold= 41% is 3.2 times the sample mean(12.8%)
Prob of RI for 30 kt RI threshold= 19% is 2.2 times the sample mean( 8.4%)
Prob of RI for 35 kt RI threshold= 11% is 2.2 times the sample mean( 5.0%)
Prob of RI for 40 kt RI threshold= 7% is 1.9 times the sample mean( 3.4%)
Member Since: August 12, 2007 Posts: 11 Comments: 2449
15. aquak9
9:59 PM GMT on September 06, 2011
and we gotta wait till what, 55 or 50? before the HH can get to TD14?
Member Since: August 13, 2005 Posts: 199 Comments: 29600
14. MiamiHurricanes09
9:54 PM GMT on September 06, 2011
Quoting TropicalAnalystwx13:


We should see that dry air disappear within the next 24-48 hours as return flow returns (lol), and moistens up the Gulf of Mexico. While it may not develop within the next 48 hours, I highly disagree that chances need to be near 50%.

We sound like Levi and Drak, except less complex, lol.
LOL, I guess we'll see. Tomorrow's Recon flight will give us a much better insight on what's occurring within 96L.
Member Since: September 2, 2009 Posts: 131 Comments: 21689
13. TropicalAnalystwx13
9:48 PM GMT on September 06, 2011
Quoting MiamiHurricanes09:
That and the monster amount of dry air located to the northwest. Look at the water vapor loop, it's going to be nearly impossible for this system to fire persistent and organized convection in those conditions.

Don't get me wrong, chances that this eventually develops into Nate are pretty good (especially when you have the ECMWF and GFS in agreement), but I just don't see it occurring in the next 48 hours...hence the 10% I'm giving it.


We should see that dry air disappear within the next 24-48 hours as return flow returns (lol), and moistens up the Gulf of Mexico. While it may not develop within the next 48 hours, I highly disagree that chances need to be near 50%.

We sound like Levi and Drak, except less complex, lol.
Member Since: July 6, 2010 Posts: 128 Comments: 35751
12. MiamiHurricanes09
9:44 PM GMT on September 06, 2011
Quoting aquak9:
you forgot to add, "..and she's the prettiest TD I've seen all summer."

:)
Yup! Gonna add it to the blog entry too lol.
Member Since: September 2, 2009 Posts: 131 Comments: 21689
11. MiamiHurricanes09
9:42 PM GMT on September 06, 2011
Quoting TropicalAnalystwx13:


The reason why there is a deteriorating satellite presentation is because daytime heating is at its peak. Come on Miami, you should know that! lol.
That and the monster amount of dry air located to the northwest. Look at the water vapor loop, it's going to be nearly impossible for this system to fire persistent and organized convection in those conditions.

Don't get me wrong, chances that this eventually develops into Nate are pretty good (especially when you have the ECMWF and GFS in agreement), but I just don't see it occurring in the next 48 hours...hence the 10% I'm giving it.
Member Since: September 2, 2009 Posts: 131 Comments: 21689
10. aquak9
9:41 PM GMT on September 06, 2011
you forgot to add, "..and she's the prettiest TD I've seen all summer."

:)
Member Since: August 13, 2005 Posts: 199 Comments: 29600
9. MiamiHurricanes09
9:39 PM GMT on September 06, 2011
Quoting Guiness:
Great blog thanks for the info.

British Virgin Islands here, what is your gut feeling for track and intensity by the time it reaches us on Saturday night? The NHC predicts a strong tropical storm, but if TD14 forms hurricane Maria sooner as you say, what further strengthening do you predict?

Thanks
I doubt she'll intensify too much between now and the time she reaches you guys, however I would be preparing for a moderate/strong category 1. I believe that the NHC intensity forecast is a little biased towards the models (which aren't showing too much intensification), hence the slower rate of intensification they're forecating. All I need to know is that dry air will be low, upper-level winds will be favorable, and that sea surface temperatures are warm. That right there is a recipe for some good intensification within a 5 day time-frame.

Plus, she's the most beautiful tropical depression I've ever seen... :)
Member Since: September 2, 2009 Posts: 131 Comments: 21689
8. TropicalAnalystwx13
9:37 PM GMT on September 06, 2011
Quoting MiamiHurricanes09:
This loop reveals a deteriorating satellite presentation. I haven't looked at surface observations in the region, however if you look on visible the spin that you see is confined mainly to the mid-levels with a lack of lower-level inflow into the meager convection.

Even though I'm sounding like a downcaster right now, lol, it's just what I'm seeing.


The reason why there is a deteriorating satellite presentation is because daytime heating is at its peak. Come on Miami, you should know that! lol.
Member Since: July 6, 2010 Posts: 128 Comments: 35751
7. MiamiHurricanes09
9:32 PM GMT on September 06, 2011
Quoting TropicalAnalystwx13:
According to MississippiWx, personal weather stations along the southern coastline of the Bay of Campeche are saying that 96L is developing a closed low, if it doesn't already have one. Additionally, buoys in the area are falling steadily. Satellite presentation is also improving steadily.

IMO, this needs to be near 50%.
This loop reveals a deteriorating satellite presentation. I haven't looked at surface observations in the region, however if you look on visible the spin that you see is confined mainly to the mid-levels with a lack of lower-level inflow into the meager convection.

Even though I'm sounding like a downcaster right now, lol, it's just what I'm seeing.
Member Since: September 2, 2009 Posts: 131 Comments: 21689
6. Guiness
9:29 PM GMT on September 06, 2011
Great blog thanks for the info.

British Virgin Islands here, what is your gut feeling for track and intensity by the time it reaches us on Saturday night? The NHC predicts a strong tropical storm, but if TD14 forms hurricane Maria sooner as you say, what further strengthening do you predict?

Thanks
Member Since: September 2, 2008 Posts: 0 Comments: 46
5. TropicalAnalystwx13
9:24 PM GMT on September 06, 2011
According to MississippiWx, personal weather stations along the southern coastline of the Bay of Campeche are saying that 96L is developing a closed low, if it doesn't already have one. Additionally, buoys in the area are falling steadily. Satellite presentation is also improving steadily.

IMO, this needs to be near 50%.
Member Since: July 6, 2010 Posts: 128 Comments: 35751
4. interstatelover7165
9:24 PM GMT on September 06, 2011
I also know a beuatiful Maria.
Member Since: August 18, 2011 Posts: 0 Comments: 994
3. aquak9
9:23 PM GMT on September 06, 2011
you really think 14's gonna grab the M name? well, yeah, then that'd be Nate in the gulf.

I know a Maria, she is beautiful, also.
Member Since: August 13, 2005 Posts: 199 Comments: 29600
2. MiamiHurricanes09
9:20 PM GMT on September 06, 2011
Quoting aquak9:
TD14 is as pretty as a pinwheel, spinning slowly out there. Haven't seen one this year that I found quite so visibly attractive.
Dang, you commented before I made the final edits lol.

And I agree with you, beautiful looking tropical depression that will probably become Maria by tonight.
Member Since: September 2, 2009 Posts: 131 Comments: 21689
1. aquak9
9:17 PM GMT on September 06, 2011
TD14 is as pretty as a pinwheel, spinning slowly out there. Haven't seen one this year that I found quite so visibly attractive.
Member Since: August 13, 2005 Posts: 199 Comments: 29600

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